1. Field of the Invention
This invention relates to glazing and, more particularly, to chromogenic glazing for use in applications, such as automobiles and display filters, where it is desirable to reversibly alter the transmission or tinting of the glass. This invention may also be used for other means of transportation glazing such as trucks, buses, boats, planes, trains, etc. and also in building glazing.
2. Related Background Art
Automobile windshields, movable and fixed side and rear windows, and divider panels between the front and the rear cabin, as well as sunroofs, employ various forms of glazing in a variety of colors and intensities. Typically, when tinted glazing is employed, the windshield and the front side windows are clear for safety reasons. Car glazing may provide for management of both ultra-violet and infra-red solar energy penetration to enhance user comfort while reducing the power requirements for air-conditioning. Besides the need to carefully control tinting so that glass used in adjacent windows does not appear to be mismatched, it is important to consider the effect that glazing color can have on passengers"" skin tones. For example, some colors, such as deep violet glazing may make the interior colors appear dull and/or strange and cause the skin tones of passengers to appear unnatural.
To adapt chromogenic glass, i.e., glass that has user-controllable transmissivity (for example see U.S. Pat. No. 6,039,390, which is incorporated by reference herein, for various technologies for user-controlled glass transmission, all of which are applicable here) for use in automobiles, it is important that the glass exhibit several characteristics:
1. Chromogenic glazing should be compatible with the color of the car""s interior.
2. Chromogenic glazing should be available in xe2x80x9cwarmxe2x80x9d tones and in xe2x80x9cneutralxe2x80x9d tones.
3. Chromogenic glazing should not acquire an unacceptable color when it is changed from clearer to a darker state under user control.
4. Chromogenic glazing should maintain an acceptable color appearance from the outside, e.g., it is preferable that all of the windows should have similar color properties while permitting the depth of coloration of the windows (and of the sunroof) to vary.
5. Chromogenic glazing for use in a windshield may be colored or bleached to a different shade or color as compared to the other windows to maintain safe, non-glaring conditions during driving.
6. Chromogenic glazing should maintain a desired state of color without consuming too much battery power when the vehicle is parked for a long period of time.
Problems With Prior Art Chromogenic Glass
When a formulation for chromogenic glass is adopted, considerable thought is given to selecting and processing the materials in order for the glass to meet a desired transmission range, durability and environmental resilience, i.e., performance over a range of temperature, typically between xe2x88x9240 to 100 C., varying humidity, and solar radiation. Electrochromic (EC) devices used in automobile glazing should not drain the battery even when left parked in the darkened state. In automobile glazing the aesthetics of color choice play an important role. Automobile manufacturers currently prefer glazing colors that are xe2x80x9cneutralxe2x80x9d or xe2x80x9cwarmxe2x80x9d so that the flesh tones of the driver and passengers and the interior colors will not be cast in an unappealing light. Certain EC materials, such as those that derive their color principally from tungsten oxide, can typically color to a blue tint and maybe undesirable in some circumstances because their color change fails to meet the neutral/warm criteria. To meet the desired characteristics, such EC materials must be modified by doping, so that they will color to a more neutral shade, but in doing so the coloration range may be compromised. Other compromises made in material selection may affect durability because of electrochemical changes in the material. In addition, glazing used in an automobile windshield may need to have different transmissivity and color characteristics as compared to the side or rear windows and sunroof. While some chromogenic devices may be available that change to a more neutral color, they may not conform to the desired transmission range required for the various locations. The chemical modification of such materials to meet these diverse applications is a daunting task.
It is therefore an object of the present invention to accommodate the different xe2x80x9ctunabilityxe2x80x9d, xe2x80x9ctransmissivityxe2x80x9d and environmental attributes required of glazing destined for diverse applications, without entailing the time and expense required to formulate a new EC material having the desired characteristics.
The above noted problems of chromogenic glass for use in various glazing applications are solved in accordance with the principles of the present invention by providing a transparent chromogenic assembly in which color changes are selectively effectable over predefined areas of the assembly that comprises a pair of facing glass substrates separated by an electrolyte. A conductive transparent coating is deposed on facing surfaces of the substrates, the conductive coating of at least one of the surfaces being interrupted to define individual areas each of which is provided with a set of busbars, advantageously of silver frit. An electrochromic electrode layer overlies at least one of the conductive layers. An insulating adhesive sealant spaces apart the substrates and insulates the busbar sets from each other and from exposure to the electrolyte and the electrochromic layer, so that each busbar set may be individually energizeable to effect a color change through a respective one of the individual areas. Advantageously, the electrochromic layer may comprise a transition metal oxide or a mixture containing at least one transition metal oxide, preferably tungsten oxide, while a counterelectrode layer on the facing surface may comprise an oxide or mixture of oxides. A preferred mixture has at least three oxides, preferably two of the three oxides are transition metals and one of them is an alkali metal. A portion of each busbar advantageously extends from the facing surface to and over a respective edge of the substrate to form a connector for the terminal electrode that provides exceptional mechanical stability.
Further in accordance with the invention, it is important to select those attributes which allow chromogenic devices to exhibit low leakage currents, e.g., by employing inorganic EC and counterelectrodes that are selected principally from the transition metal oxides, examples being at least consisting in part of tungsten oxide, molybdenum oxide as EC electrodes and consisting in part of vanadium oxide, nickel oxide, manganese oxide, niobium oxide and titanium oxide for counter electrodes, and by using sulfolane or its derivatives in full or part as the solvent and/or plasticizer in the electrolyte when a solid polymer matrix electrolyte is used. Further, the water content of the electrolyte is preferably lower than 2000 ppm, more preferably lower than 100 ppm and most preferably as low as 10 ppm. The EC and the counterelectrodes may be further doped by alkali metal oxides such as Li, Na, Ba, Ca, K, Cs and Rb oxides.
According to another aspect of the invention, in one illustrative embodiment, a transparent chromogenic assembly is provided which comprises an active component layer and a passive component layer in which the active component layer is selected from the group consisting of electrochromic, liquid crystal, user-controllable-photochromic, polymer-dispersed-liquid crystal or suspended particle devices and the passive component layer is selected from the group consisting of substrates or covers for the active layer, the active and the passive layers being chosen so that the color and the transmissivity of the passive layer accommodates the range of color change and transmissivity of the active layer to maintain the transmitted color of the assembly in a warm or neutral shade, where warm colors correspond on the L*C*h color sphere scale to C having an approximate value between 15 and 45, preferably between 18 and 30; h having a value between 20 and 115, preferably between 40 and 100, and L having a value dictated by the desired degree of glass darkness or preferred degree of photopic transmission. A preferred counterelectrode composition consists of Li, Ni and Mn oxides to facilitate obtaining the desired color change as an intrinsic attribute of the EC device.
Yet another embodiment of this invention is directed to a chromogenic device with controlled variation of the area subject to coloration. This device includes a pair of facing transparent substrates defining a cavity enclosing an electrolyte medium. Each of the facing surfaces of the substrates has a conductive transparent coating. In addition, an electrochromic layer is disposed on at least one of the conductive transparent coatings. Significantly, each conductive transparent coating will have at least two bus bars in contact therewith and the two bus bars are positioned in a spaced-apart relationship that defines a portion of the device in which the area of coloration of the device is variably controlled. Of course if the chromogenic device includes two or more portions as in the previously described chromogenic assembly, one or more of those portions may be designed to allow controlled variation of the area of each portion subject to coloration. The chromogenic device will also include a controller that provides a means for controlling the area of coloration by varying a voltage drop across the portion of the device being controlled. The controller will generally include a switch for applying a voltage between a first of said two bus bars contacting a first of the transparent conductive coatings and an opposing first of said two bus bars contacting a second of the transparent conductive coatings. The controller will also preferably include a variable resistor communicating between a second of said two bus bars contacting the first transparent conductive coating and a second of said two bus bars contacting the second transparent conductive coating. In a preferred embodiment, the area of the portion of the device subject to coloration may be controlled by varying the resistance value of the variable resistor.
Another embodiment of this invention is directed to a chromogenic device having both coloration and heating capability. This device is similar in structure to above described device that provides for controlled variation of the area of coloration, but its controller provides a means to selectively apply a voltage to color the device or heat the device. Preferably, the controller of this device includes an electrical circuit that may be selectively controlled (i) to cause coloration of the device by creating a voltage potential between at least one of said bus bars contacting a first of the transparent coatings and at least one of the two bus bars contacting a second of the transparent coatings and (ii) to cause heating of the device by creating a voltage potential between at least the two bus bars contacting at least one of the conductive transparent coatings. Of course, if desirable a controller may be fashioned to provide the ability to heat the device, color the device and provide control of the area of the device subject to coloration.